Chemical-mechanical polishing device, damascene wiring forming device, and damascene wiring forming method

ABSTRACT

In a chemical mechanical polishing apparatus in accordance with the present invention, a material having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm is used as an elastic member ( 16 ) arranged between a polishing pad ( 12 ) and a platen ( 36 ). Therefore, both flatness and uniformity of a wafer can be sufficiently improved.

TECHNICAL FIELD

The present invention relates to a polishing apparatus and a polishingmethod in which a metal film surface formed on a semiconductor substrateis polished by a chemical mechanical approach.

BACKGROUND ART

A planarizaion process of a wafer (semiconductor substrate) in amanufacturing process is important to attain a higher integration of asemiconductor device. A CMP (Chemical Mechanical Polishing) apparatus iswidely used as an apparatus planarizing a wafer. In a CMP apparatus, forexample, while polishing slurry is supplied to a wafer to be polished, ametal film and the like on the wafer are polished by contact with apolishing pad.

Now, in order to selectively polish protruding portions (improveflatness) of an insulating film, a metal film and the like on a wafer,deformation of a polishing pad surface needs to be suppressed and a highhardness of the polishing pad is required. On the other hand, in orderto perform uniform polishing on the entire semiconductor wafer (improveuniformity), flexibility sufficient to conform warp of the wafer isrequired for the polishing pad. Therefore, since there is a trade-offbetween flatness and uniformity in selecting a polishing pad, it isdifficult to ensure both flatness and uniformity of polishing. Thus, forthe purpose of improving both flatness and uniformity of the wafer, sucha polishing pad is employed that has a two-layer structure formed with ahard material arranged in an upper layer in contact with the wafer to bepolished and a soft material arranged in a lower layer thereof.

A wafer holding (fixing) method will now be described. Generally, in aCMP apparatus, a wafer is held using a vacuum chuck (vacuum suction), abacking film (backing pad) and the like. Advantages of using a vacuumchuck include: easiness of wafer replacement (attachment and removal);secure and firm holding of wafer; and elimination of wafer warp. As adisadvantage, the use of the aforementioned polishing pad having thetwo-layer structure described above cannot accommodate macroscopicthickness variations of the wafer, resulting in a poor polishinguniformity.

On the other hand, although the use of a backing pad is inferior ineasiness of wafer attachment and removal and secure holding of wafer, ithas an advantage in that wafer warp, thickness variations and the likecan be accommodated (reduced) to some extent as the backing pad itselfhas a good elasticity. As a result, macroscopic undulations of the wafercan be reduced to some extent and poorer polishing uniformity can beprevented to some extent. Therefore, holding a wafer using a backing padis presently common. A polishing apparatus using a backing pad as waferholding means and using a polishing pad having the aforementionedtwo-layer structure (hard material and soft material) is disclosed forexample in Japanese Patent Laying-Open Nos. 10-138123, 9-321001,9-260318, 7-266219 and 7-297195.

The present situation of the conventional polishing method has beendescribed above. In conclusion, the conventional CMP apparatus cannotimprove both flatness and uniformity in a wafer sufficiently. Thisproblem is outstanding particularly in case of polishing a damascenestructure.

DISCLOSURE OF THE INVENTION

The present invention is made in view of the situation described above.A first object of the present invention is to provide a chemicalmechanical polishing apparatus capable of sufficiently improving bothflatness and uniformity of polishing even with a vacuum chuck excellentin easiness of wafer attachment and removal and secure holding of awafer.

A second object of the present invention is to provide a damasceneinterconnection forming apparatus and method in which an accuratedamascene interconnection can be formed by using a polishing apparatusrealizing good flatness and uniformity.

In order to achieve the above objects, a chemical mechanical polishingapparatus in accordance with the present invention is applied to anapparatus including: a substrate holding table holding a semiconductorsubstrate by vacuum suction; a polishing pad being in contact with thesemiconductor substrate; a platen holding the polishing pad; and anelastic member arranged between the polishing pad and the platen. It ischaracterized in that a material having a hardness defined by JISstandard K6301 (A type) of 10-40 and a thickness of 5-30 mm is used asthe elastic member.

A damascene interconnection forming apparatus in accordance with thepresent invention is applied to a damascene interconnection formingapparatus forming an insulating film on a semiconductor substrate,forming a recessed portion in a prescribed region of the insulatingfilm, forming a barrier metal film on a surface of the insulating filmincluding the recessed portion, and forming a metal interconnection filmon the barrier metal film to completely fill in at least the recessedportion, followed by polishing the metal film and the barrier metal filmuntil the insulating film is exposed in a region other than the recessedportion. It is characterized by including: first polishing means forperforming a first polishing step of polishing the metal interconnectionfilm until the barrier metal film is exposed in the region other thanthe recessed portion; and second polishing means for performing a secondpolishing step of polishing the barrier metal film until the insulatingfilm is exposed in the region other than the recessed portion.Furthermore, the first polishing means includes: a substrate holdingtable holding the semiconductor substrate by vacuum suction; a polishingpad being in contact with the semiconductor substrate; a platen holdingthe polishing pad; and an elastic member arranged between the polishingpad and the platen and having a hardness defined by JIS standard K6301(A type) of 10-40 and a thickness of 5-30 mm. In addition, the secondpolishing means includes: a substrate holding table holding thesemiconductor substrate by vacuum suction; a polishing pad being incontact with the semiconductor substrate; a platen holding the polishingpad; and an elastic member arranged between the polishing pad and theplaten and having a hardness defined by JIS standard K6301 (A type) ofat least 50.

A damascene interconnection forming method in accordance with thepresent invention is applied to a damascene interconnection formingmethod of forming an insulating film on a semiconductor substrate,forming a recessed portion in a prescribed region of the insulatingfilm, forming a barrier metal film on a surface of the insulating filmincluding the recessed portion, and forming a metal interconnection filmon the barrier metal film to completely fill in at least the recessedportion, followed by polishing the metal film and the barrier metal filmuntil the insulating film is exposed in a region other than the recessedportion. It is characterized by including: a first polishing step ofpolishing the metal interconnection film until the barrier metal film isexposed in the region other than the recessed portion using firstpolishing means; and a second polishing step of polishing the barriermetal film until the insulating film is exposed in the region other thanthe recessed portion using second polishing means. Furthermore, thefirst polishing means includes: a substrate holding table holding thesemiconductor substrate by vacuum suction; a polishing pad being incontact with the semiconductor substrate; a platen holding the polishingpad; and an elastic member arranged between the polishing pad and theplaten and having a hardness defined by JIS standard K6301 (A type) of10-40 and a thickness of 5-30 mm. In addition, the second polishingmeans includes: a substrate holding table holding the semiconductorsubstrate by vacuum suction; a polishing pad being in contact with thesemiconductor substrate; a platen holding the polishing pad; and anelastic member arranged between the polishing pad and the platen andhaving a hardness defined by JIS standard K6301 (A type) of at least 50.

In the damascene interconnection forming apparatus and method describedabove, preferably, the first polishing means and the second polishingmeans are implemented by a single chemical mechanical polishingapparatus. More specifically, the polishing apparatus includes: asubstrate holding table holding the semiconductor substrate by vacuumsuction; first and second platens arranged in positions opposing thesubstrate holding table in a polishing operation; a first polishing padarranged on the first platen; a second polishing pad arranged on thesecond platen; a first elastic member arranged between the first platenand the first polishing pad and having a hardness defined by JISstandard K6301 (A type) of 10-40 and a thickness of 5-30 mm; and asecond elastic member arranged between the second platen and the secondpolishing pad and having a hardness defined by JIS standard K6301 (Atype) of at least 50. In performing the first polishing step, thesubstrate holding table is arranged in a position opposing the firstplaten, and in performing the second polishing step, the substrateholding table is arranged in a position opposing the second platen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view (with a partial cross section) showing aconfiguration of a CMP apparatus in accordance with the presentinvention with a polishing pad fixed by a mounting technique.

FIG. 2 is a cross sectional view showing a configuration of a main partof the CMP apparatus in accordance with the present invention with thepolishing pad adhesively fixed to a platen.

FIGS. 3A to 3C are cross sectional views showing the steps of adamascene interconnection forming method in accordance with the presentinvention, in which FIG. 3A is a state before polishing, FIG. 3B is astate after a first polishing step and FIG. 3C is a state after a secondpolishing step.

FIG. 4 is an illustration showing points for measuringwithin-wafer-surface-uniformity (polishing uniformity) in accordancewith the present invention.

FIG. 5 is a plane view showing a configuration of a main part of apolishing apparatus (a platen and a wafer holding table) in accordancewith the present invention.

FIG. 6 is a side view of the apparatus shown in FIG. 5 with a partialcross section.

FIG. 7 is a plane view showing the configuration of the main part ofanother type of polishing apparatus (the platen and the wafer holdingtable) in accordance with the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention is applied to a case where a metal interconnectionlayer having a narrow width (less than 200 μm) of a recessed portion ispolished, in a type of CMP apparatus in which a wafer is basically fixedby a vacuum chuck.

FIG. 1 shows a configuration of a CMP apparatus according to a firstembodiment of the present invention. This CMP apparatus includes apolishing pad 12 in contact with a wafer 10 to be polished, a platen 14with polishing pad 12 attached thereto, an elastic member 16 arrangedbetween polishing pad 12 and platen 14, a wafer stage 20 holding wafer10, a retainer 18 fixed on wafer stage 20, and a wafer turn table 22rotatably supporting wafer stage 20. The main feature of the presentinvention is in a setting of hardness and thickness of elastic member16. It is noted that a specific setting value of elastic member 16 willbe described later.

Elastic member 16 is formed like a ring (doughnut-shaped) having a holeat the center thereof and fixed on platen 14 by a double-faced tape andthe like. Elastic member 16 is set on platen 14 without letting-in airtherebetween. Normally, once elastic member 16 is set on platen 14, itis not frequently replaced. Polishing pad 12 is also formed like a ring(doughnut-shaped) and fixed on a bottom face of platen 14 by an innerring 24, an outer peripheral ring 26 and bolts 28, 30.

Wafer stage 20 is provided in a rotatable manner on wafer turn table 22.Retainer 18 is fixed on wafer stage 20 and wafer 10 is fixed on waferstage 20 by a vacuum chuck. Platen 14, wafer turn table 22 and waferstage 20 each are rotated about axes A-A′, B-B′ and C-C′. At the centerof platen 14, a slurry supply hole 32 is provided to extend vertically,and prescribed slurry is supplied from this slurry supply hole 32 duringa polishing operation.

Polishing pad 12 is fixed on platen 14 by a so-called mountingtechnique. Specifically, without using adhesive and the like, it isfixed by fastening the aforementioned bolts 28 and 30 only at an outerperipheral portion and an inner peripheral portion. It is noted that inthe present invention a method of fixing a polishing pad is not limitedto the mounting technique and a variety of techniques including anadhesive technique (FIG. 2) and the like can be employed.

In a polishing operation, wafer 10 is fixed on wafer stage 20 by avacuum chuck, and platen 14, wafer turn table 22 and wafer stage 20 eachare driven to rotate. Thereafter, while slurry is supplied from slurrysupply hole 32, platen 14 is brought down and polishing pad 12 ispressed against a polished surface of wafer 10 at a prescribed pressurefor polishing.

FIG. 2 shows an example in which a polishing pad is adhesively fixed ona platen. In this example, an elastic member 38 is adhesively fixed on aplaten 36, and a polishing pad 40 is adhesively fixed on elastic member38. Wafer 10 is fixed on a bottom surface of wafer holding table 42 byvacuum suction. Inside wafer holding table 42, a plurality of holes 44for evacuation are formed.

Elastic member 16, 38 in accordance with the present invention is set tohave a thickness defined by JIS standard K6301 (A type) of 10-40 and athickness of 5-30 mm. In the following, grounds for this (experimentaldata) will be described. It is noted that such a polishing pad can beused that has a hardness defined by JIS standard K6301 (A type) of 90 ormore and a thickness of 0.5-2 mm. In the experiment below, IC 1000manufactured by Rodel Inc. in USA (having a hardness of 95 and athickness of about 1.3 mm) was used.

1. Evaluation for Hardness of the Elastic Member

An experiment was performed on changes of flatness and uniformity inwafer polishing with respect to the hardness of elastic member 16 or 38.The experiment was performed on a sample (wafer) shown in FIG. 3A. Thewafer had a pattern by forming a thermal oxide film (insulating film) 46having a thickness of 5000 Å on a substrate, forming a recessed portionhaving a width of 10 μm-5 mm and a depth of 4500 Å (to be aninterconnection portion after completing polishing) in a prescribedregion, forming a Ta film (barrier metal film) 48 thereon having athickness of 200 Å, forming a Cu seed film 50 thereon having a thicknessof 1000 Å, and further forming Cu plating 52 (metal interconnectionfilm) thereon having a thickness of 1 μm. The pattern used in theexperiment had a line and space of a 10 mm length with a space set at 5mm. The lines (recessed portions) as used herein had different widths(10 μm-5 mm). The thickness of the elastic body was 10 mm. Furthermore,a polishing rate was set at a value of 6000 Å/min when an entirely flatfilm (mat film) of Cu was polished at a pressure of 300 g/cm².

(1) Flatness Evaluation

In a flatness evaluation, polishing (in one step) was performed untiloxide film 46 in the aforementioned pattern surface was exposed, and aninterconnection thickness decreasing amount (dishing) after polishingwas measured in the interconnection portions having a variety of widths.The experimental results are shown in Table 1. It is noted that in thetable the hardness is a value defined by JIS standard K6301 (A type) anddishing amount is expressed in A. Furthermore, in the table,“IC1000/400” means IC1000/400 manufactured by Rodel Inc. in USA. This isa polishing pad with two-layer structure conventionally commonly used,using IC1000 (having a hardness of 95 in conformity with JIS-K6301) as ahard material of an upper layer (corresponding to the polishing pad ofthe present invention) and using SUBA400 (having a hardness of 55-66 inconformity with JIS-K6301) as a soft material of a lower layer(corresponding to the elastic member of the present invention).

TABLE 1 interconnection width hardness 10 μm 20 50 100 200 500 1 mm 2 mm5 mm 5 200 400 800 1700 2000 3500 3800 4000 4500 10 50 100 100 300 6001800 2000 3200 4500 20 50 100 100 300 500 1500 1700 1800 4500 40 50 100100 300 500 1300 1500 1700 4500 60 50 100 100 300 500 1200 1300 15004500 IC 1000/400 50 100 100 300 400 1100 1200 1400 3500

As is clear from the Table 1 above, good flatness (low dishing amount)is obtained when a hardness is 10 or more. It is noted that in a casewhere an interconnection width (that is, a width of the recessed portionformed in insulating film 46) is 500 μm or more even with a hardness of10 or more, flatness is deteriorated. This is not a significant problem,however, since an actual width of the metal interconnection layer is notmore than 200 μm.

(2) Uniformity Evaluation

Polishing uniformity within a wafer surface was determined with elasticmember 16 or 38 having a hardness defined by JIS standard K6301 (A type)between 5 and 90. As indicated by × in FIG. 4, determination ofuniformity “δ” was performed by measuring a film thickness X_(i) attwenty-five points on two straight lines intersecting through the centerof wafer 53, based on the following equations.

Film thickness: X _(i)(i=1-25)

Average film thickness: X={fraction (1/25)}·ΣX _(i)

Within-wafer-surface-uniformity: δ=1/X·{square root over ( )}({fraction(1/25)}·Σ(X−X _(i))²)×100

The experimental results are shown in Table 2.

TABLE 2 hardness 5 10 20 40 60 90 IC 1000/400 uniformity 5.3 3.8 3.5 3.710.8 15.3 20.4

As is clear from the table above, good uniformity is obtained when ahardness of elastic member 16, 38 is between 5 and 40, particularlybetween 10 and 40.

2. Evaluation for the Thickness of the Elastic Member

An experiment was performed on changes of flatness and uniformity inwafer polishing with respect to the thickness of elastic member 16 or38. Similar to the case of the hardness of the elastic member, theexperiment was performed on a sample (wafer) shown in FIG. 3A.

(1) Flatness Evaluation

In a flatness evaluation, polishing (in one step) was performed untiloxide film 46 in the aforementioned pattern surface was exposed and aninterconnection thickness decreasing amount (dishing) after polishingwas measured in an interconnection portion having a width of 200 μm. Theexperimental results are shown in Table 3 in a range of a thickness of 3mm-60 mm and a hardness of 10-40. It is noted that in the table, thehardness is a value defined by JIS standard K6301 (A type) and a dishingamount is expressed in Å.

TABLE 3 thickness hardness 3 mm 5 10 20 30 40 60 10 600 600 600 600 9001300 20 500 500 500 500 500 800 1100 40 500 500 500 500 800 1000

As is clear from Table 3, good flatness is obtained when elastic member16 or 38 has a thickness of not less than 3 mm and not more than 30 mm.

(2) Evaluation for Within-wafer-surface-uniformity

The experiment on a uniformity evaluation was performed in the samecondition as that of the flatness described above. Specifically,polishing (in one step) was performed until oxide film 46 in the patternsurface was exposed, and uniformity after polishing in theinterconnection portion having a width of 20 μm was measured. Theexperimental results are shown in Table 4 in a range of a thickness of 3mm-60 mm and a hardness of 10-40. It is noted that determination ofuniformity “δ” was performed by measuring film thickness X_(i) attwenty-five points on two straight lines intersecting through the centerof wafer 53 (FIG. 4), based on the following equations.

Film thickness: X _(i)(i=1-25)

Average film thickness: X={fraction (1/25)}·ΣX _(i)

Within-wafer-surface-uniformity: δ=1/X·{square root over ( )}({fraction(1/25)}·Σ(X−X _(i))²)×100

TABLE 4 thickness hardness 3 mm 5 10 20 30 40 60 10 6.8 4.2 3.8 4.8 5.27.6 20 10.8 4.5 3.5 3.5 3.2 4.7 6.2 40 12.3 4.7 3.7 3.1 5.3 7.5

As is clear from Table 4, good uniformity is obtained when elasticmember 16 or 38 has a thickness of not less than 5 mm and not more than30 mm.

Considering the experimental results shown in Tables 1 to 4 on thewhole, good flatness and uniformity is obtained when elastic member 16or 38 has a hardness of 10-40 (JIS standard K6301 A type) and athickness of 5 mm-30 mm.

Next, another embodiment of the present invention will be described. Inthis embodiment, polishing of the damascene interconnection layer isperformed in two steps. Specifically, polishing is performed until Tafilm 48 is exposed in a first step and polishing is performed untiloxide film 46 is exposed in a second step.

Flatness evaluation (experimental) results are shown in Table 5 in acase where the damascene interconnection layer is polished in two steps.In this experiment, in the first polishing step, elastic member 16 or 38for use had a hardness of 10 and 20 and a thickness of 10 mm, and otherconditions were similar to those in the embodiment above (the exampleusing one step for polishing). In the second polishing step, IC1000/400manufactured by Rodel Inc. in USA was used as the polishing pad, and thesame slurry as in the first polishing step and different slurry (havinga selective ratio between Cu and Ta lower than that of the firstpolishing step) were used. Here, IC1000/400 manufactured by Rodel Inc.in USA means that IC1000 (a hardness of 95 in compliance with JIS-K6301)is used as a hard material of an upper layer (corresponding to thepolishing pad) and SUBA400 (a hardness of 55-66 in compliance withJIS-K6301) is used as a soft material of a lower layer (corresponding tothe elastic member).

In a flatness evaluation, an interconnection thickness decreasing amount(dishing) after polishing in the interconnection portion having a widthof 200 μm was measured. In the experiment, the hardness of the elasticmember (16 or 38) for use in the first polishing step was set at 10, 20.Furthermore, data (the experimental data in one step as described above)is shown as a comparative example where polishing of the damasceneinterconnection layer (FIGS. 3A-3C) was performed in one step. It isnoted that in Table 5, the hardness is a value defined by JIS standardK6301 (A type) and a dishing amount is expressed in Å.

TABLE 5 elastic body for first step slurry 10 20 IC 1000/400 same infirst and second steps 400 400 — different between first and secondsteps 300 300 — comparative example (only first step) 600 500 400

As is clear from Table 5, polishing in two steps (a first polishing stepand a second polishing step) improves the flatness as compared withpolishing up to the oxide film in one step. Using different slurrybetween a first polishing step and a second polishing step furtherimproves the flatness.

FIGS. 5 and 6 show a configuration of a main part of a CMP apparatus (aplaten and a wafer holding member) used to polish a damasceneinterconnection layer in two steps (a first polishing step and a secondpolishing step). FIG. 5 is a plane view and FIG. 6 is a side view (witha partial cross section). In this embodiment, two different platens 54and 56 are used to polish the damascene interconnection. A first platen54 holds a first polishing pad 62. A first elastic member 58 is arrangedbetween first platen 54 and polishing pad 62. A second platen 56 holds asecond polishing pad 64. A second elastic member 60 is arranged betweensecond platen 56 and polishing pad 64.

It is noted that for the purpose of using terms consistently, in case ofa polishing pad having a two-layer structure such as IC1000/400manufactured by Rodel Inc. in USA used in the experiment describedabove, an upper layer formed of a hard material being in contact with awafer to be polished will be referred to as “polishing pad” and a lowerlayer formed of a soft material positioned between the upper layer andthe platen will be referred to as “elastic member”. Furthermore, firstpolishing pad 62 and second polishing pad 64 can be used each having ahardness defined by JIS standard K6301 (A type) of not less than 90 anda thickness of 0.5 mm-2 mm. For example, IC1000 manufactured by RodelInc. in USA can be used as polishing pad 62, 64.

The CMP apparatus shown in FIGS. 5 and 6 is provided with a single waferholding table 66, and a wafer 68 is hold by vacuum suction. Waferholding table 66 can be moved between a position opposing first platen54 and a position opposing second platen 56 by a robot arm 70.

First platen 54 is used in the first polishing step (polishing untilbarrier metal 48 is exposed), and first elastic member 58 for use has ahardness defined by JIS standard K6301 (A type) of 10-40 and a thicknessof 5-30 mm. On the other hand, second platen 56 is used in the secondpolishing step (polishing until oxide film 46 is exposed), and secondelastic member 60 for use has a hardness defined by JIS standard K6301(A type) of not less than 50.

In the CMP apparatus shown in FIGS. 5 and 6, in a case where polishingis performed on the damascene interconnection structure shown in FIGS.3A-3C, wafer holding table 66 is arranged in a position opposing(directly above) first platen 54 by operating robot arm 70, and as shownin FIG. 3B, Cu film 52 and Cu seed film 50 are polished until Ta film 48is exposed (the first polishing step). Next, wafer holding table 66 isarranged in a position opposing (directly above) second platen 54 byoperating robot arm 70, and as shown in FIG. 3C, Ta film 48 is polisheduntil thermal oxide film pattern 46 is exposed (the second polishingstep).

FIG. 7 shows another example of the CMP apparatus (the platens and thewafer holding members) used to polish the damascene interconnectionlayer (FIGS. 3A-3C) in two steps (a first polishing step and a secondpolishing step). In this example, a single, first platen 72 for use inthe first polishing step and two, second platens 74 and 76 for use inthe second polishing step are provided to polish the damasceneinterconnection. First platen 72 holds first polishing pad 62 and allowstwo wafers to be polished at the same time. First elastic member 58 isarranged between first platen 72 and polishing pad 62. Each secondplaten 74, 76 has second polishing pad 64. Second elastic member 60 isarranged between second platen 74, 76 and polishing pad 64.

In the CMP apparatus shown in FIG. 7, two, second platens 74 and 76 arerespectively provided with wafer holding tables 82 and 84, and the waferis held by vacuum suction. Wafer holding table 82 can be moved between aposition opposing first platen 72 and a position opposing second platen74 by a robot arm 78. Furthermore, wafer holding table 84 can be movedbetween a position opposing first platen 72 and a position opposingsecond platen 76 by a robot arm 80.

First platen 72 is used in the first polishing step (polishing until thebarrier metal is exposed) and has a structure shown in FIG. 2.Specifically, first elastic member 38 is interposed between polishingpad 40 and platen 36. Furthermore, the elastic member for use has ahardness defined by JIS standard K6301 (A type) of 10-40 and a thicknessof 5-30 mm. On the other hand, second platen 74 is used in the secondpolishing step (polishing until the oxide film is exposed), and thesecond elastic member for use has a hardness defined by JIS standardK6301 (A type) of not less than 50.

In the CMP apparatus shown in FIG. 7, in a case where the damascenestructure shown in FIGS. 3A-3C is polished, wafer holding tables 82 and84 are arranged in positions opposing (directly above) first platen 72by operating robot arms 78 and 80, and as shown in FIG. 3B, Cu film 52and Cu seed film 50 are polished until Ta film 48 is exposed (the firstpolishing step). Next, wafer holding tables 82 and 84 are arranged inpositions opposing (directly above) second platens 74 and 76 byoperating robot arms 78 and 80, and as shown in FIG. 3C, Ta film 48 ispolished until thermal oxide film pattern 46 is exposed (the secondpolishing step).

A method of polishing the damascene interconnection layer (FIGS. 3A-3C)in two steps (a first polishing step and a second polishing step)includes a method with a plurality of platens and the respective waferholding tables corresponding to the platens within one CMP apparatus, inaddition to the methods shown in FIGS. 5, 6 and 7. In this case, in afirst polishing step, a first wafer holding table sucks and holds awafer and polishing is performed using a polishing pad attached to acorresponding first platen. Thereafter, the wafer is transferred fromthe first holding table to a second holding table using a robot arm, anda second polishing step is performed using a polishing pad attached to asecond platen.

Other methods include a method with CMP apparatuses separately providedto perform the first and second polishing steps. Still another methodmay include a method using the same CMP apparatus and the same platenfor the first and second polishing steps. In this case, the firstpolishing step is initially performed on a prescribed number (100, etc.)of wafers. The second polishing step is thereafter performed byreplacing the elastic member arranged under the polishing pad.

While the embodiments of the present invention have been describedabove, the present invention is not limited to these embodiments and maybe changed within a scope of technical concepts illustrated in theclaims.

Industrial Applicability

In accordance with the present invention, since a material having ahardness defined by JIS standard K6301 (A type) of 10-40 and a thicknessof 5-30 mm is used as an elastic member, both flatness and uniformity ofa wafer can effectively be improved even if the wafer is held by vacuumsuction. Therefore, advantageously, an accurate damasceneinterconnection can be formed.

What is claimed is:
 1. A chemical mechanical polishing apparatusplanarizing a surface of a metal film formed on a semiconductorsubstrate (10), comprising: a substrate holding table (42) holding saidsemiconductor substrate by vacuum suction; a polishing pad (12) being incontact with said semiconductor substrate; a platen (36) holding saidpolishing pad; and an elastic member (16) arranged between saidpolishing pad and said platen, wherein said elastic member has ahardness defined by JIS standard K6301 (A type) of 10-40 and a thicknessof 5-30 mm.
 2. A damascene interconnection forming apparatus forming aninsulating film (46) on a semiconductor substrate (10), forming arecessed portion in a prescribed region of the insulating film, forminga barrier metal film (48) on a surface of the insulating film includingthe recessed portion, and forming a metal interconnection film (52) onsaid barrier metal film to completely fill in at least said recessedportion, followed by polishing said metal film and said barrier metalfilm until said insulating film is exposed in a region other than saidrecessed portion, comprising: first polishing means for performing afirst polishing step of polishing said metal interconnection film untilsaid barrier metal film is exposed in the region other than saidrecessed portion; and second polishing means for performing a secondpolishing step of polishing said barrier metal film until saidinsulating film is exposed in the region other than said recessedportion, wherein said first polishing means includes a substrate holdingtable holding said semiconductor substrate by vacuum suction, apolishing pad being in contact with said semiconductor substrate, aplaten holding said polishing pad, and an elastic member arrangedbetween said polishing pad and said platen and having a hardness definedby JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm, andsaid second polishing means includes a substrate holding table holdingsaid semiconductor substrate by vacuum suction, a polishing pad being incontact with said semiconductor substrate, a platen holding saidpolishing pad, and an elastic member arranged between said polishing padand said platen and having a hardness defined by JIS standard K6301 (Atype) of at least
 50. 3. The damascene interconnection forming apparatusaccording to claim 2, wherein said first and second polishing means areincluded in a single chemical mechanical polishing apparatus, thepolishing apparatus includes a substrate holding table (66) holding saidsemiconductor substrate (10) by vacuum suction, first and second platens(54, 56) each arranged in a position opposing said substrate holdingtable in a polishing operation, a first polishing pad (62) arranged onsaid first platen (54), a second polishing pad (64) arranged on saidsecond platen (56), a first elastic member (58) arranged between saidfirst platen and said first polishing pad and having a hardness definedby JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm, anda second elastic member (60) arranged between said second platen andsaid second polishing pad and having a hardness defined by JIS standardK6301 (A type) of at least 50, and in performing said first polishingstep, polishing is performed using said first polishing pad by arrangingsaid substrate holding table in a position opposing said first platen,and in performing said second polishing step, polishing is performedusing said second polishing pad by arranging said substrate holdingtable in a position opposing said second platen.
 4. The damasceneinterconnection forming apparatus according to claim 3, wherein saidchemical mechanical polishing apparatus includes one said first platen(54), a plurality of said second platens, and said substrate holdingtables as many as said second platens (56).
 5. A damasceneinterconnection forming method of forming an insulating film (46) on asemiconductor substrate (10), forming a recessed portion in a prescribedregion of the insulating film, forming a barrier metal film (48) on asurface of the insulating film including the recessed portion, andforming a metal interconnection film (52) on said barrier metal film tocompletely fill in at least said recessed portion, followed by polishingsaid metal film and said barrier metal film until said insulating filmis exposed in a region other than said recessed portion, comprising: afirst polishing step of polishing said metal interconnection film untilsaid barrier metal film is exposed in the region other than saidrecessed portion using first polishing means; and a second polishingstep of polishing said barrier metal film until said insulating film isexposed in the region other than said recessed portion using secondpolishing means, wherein said first polishing means includes a substrateholding table (66) holding said semiconductor substrate by vacuumsuction, a polishing pad (62, 64) being in contact with saidsemiconductor substrate, a platen (54, 56) holding said polishing pad,and an elastic member (58, 60) arranged between said polishing pad andsaid platen and having a hardness defined by JIS standard K6301 (A type)of 10-40 and a thickness of 5-30 mm, and said second polishing meansincludes a substrate holding table holding said semiconductor substrateby vacuum suction, a polishing pad being in contact with saidsemiconductor substrate, a platen holding said polishing pad, and anelastic member arranged between said polishing pad and said platen andhaving a hardness defined by JIS standard K6301 (A type) of at least 50.6. The damascene interconnection forming method according to claim 5,wherein said first and second polishing means are included in a singlechemical mechanical polishing apparatus, the polishing apparatusincludes a substrate holding table (66) holding said semiconductorsubstrate (10) by vacuum suction, first and second platens (54, 56) eacharranged in a position opposing said substrate holding table in apolishing operation, a first polishing pad (62) arranged on said firstplaten (54), a second polishing pad (64) arranged on said second platen(56), a first elastic member (58) arranged between said first platen andsaid first polishing pad and having a hardness defined by JIS standardK6301 (A type) of 10-40 and a thickness of 5-30 mm, and a second elasticmember (60) arranged between said second platen and said secondpolishing pad and having a hardness defined by JIS standard K6301 (Atype) of at least 50, and in performing said first polishing step,polishing is performed using said first polishing pad by arranging saidsubstrate holding table in a position opposing said first platen, and inperforming said second polishing step, polishing is performed using saidsecond polishing pad by arranging said substrate holding table in aposition opposing said second platen.
 7. The damascene interconnectionforming method according to claim 6, wherein said chemical mechanicalpolishing apparatus includes one said first platen (54), a plurality ofsaid second platens, and said substrate holding tables as many as saidsecond platens (56).